Background of the Invention
1. Field of the Invention
The present invention relates to high concentration ammonium sulfate suspensions in oil that exhibit acceptable physical stability during normal storage conditions, and that upon dilution in a suitable volume of water, are suitable for application to plants as herbicidal compositions, adjuvants in herbicidal compositions, or fertilizers, or that may be used for other purposes.
2. Description of the Related Art
When growing crops in a field, it is important to kill or control the growth of undesirable plants (weeds) in the field. If not controlled, the weeds compete with crop plants for essential resources such as soil nutrients, water and sunlight. By removing a fraction of the resources or otherwise reducing the availability of these resources to crop plants, the weeds restrict crop growth, resulting in loss of crop yield.
Timely and judicious use of herbicides can provide weed control to minimize crop losses and production costs. Herbicides such as glyphosate (N-phosphonomethyl glycine) and many others are useful for control of a large variety of weeds. When used in an herbicidal composition, glyphosate is generally in the form of one of its various salts in solution, preferably an aqueous solution.
Adjuvants are materials that enhance the action of herbicides by promoting adsorption and translocation and by complexing antagonistic metal ions in the water used to make the herbicide solution. Ammonium sulfate has been known as an adjuvant. for several decades (U. Suwunnamek and D Penner, Weed Research, 15, 13-19 (1975)). It is perhaps the most important commercial adjuvant and is also widely used as a fertilizer. Several different types of oils have also been found to act as adjuvants. However, mineral oil has been reported to decrease the activity of glyphosate herbicide (H. De Ruiter et al., Cent. Agrobiol. Res., Wageningen, Neth., Meded. Fac., Landbouwwet, Rijksuniv. Gent, 52(3B) 1217-24 (1987)).
Herbicides are typically applied to field crops by spraying an aqueous mixture of several components. Polymers that inhibit spray drift, defoamers, and other chemicals that enhance the performance of an herbicide are sometimes mixed with the ammonium sulfate. All solid components of a mixture are typically ground to a small particle size in order to reduce the time required to dissolve. Growers and contract applicators use a xe2x80x9cmixxe2x80x9d tank to prepare the herbicide mixture. A typical mix consists of about 800 pounds of water, 8 to 17 pounds of herbicide, and 8 to 17 pounds of dry adjuvant. The result is a 1% or 2% solution of herbicide and 1% or 2% of adjuvant. The typical tank has relatively poor mixing and the applicator, whether using a truck or airplane, usually has little time to wait for dissolution. Even small particles tend to fall to the bottom of the mix tank in clumps and are sometimes slow to dissolve. In addition, these dry adjuvants generate undesirable dusty conditions when the package is opened and poured into the mix tank. Therefore, liquid preparations are preferable.
However, many liquids suffer disadvantages because of low product concentration. Freight, handling, and packaging costs become a substantial part of the total product cost. It would be desirable to have ammonium sulfate in a high concentration liquid form, but because storage temperature conditions vary, the highest practical concentration of ammonium sulfate in aqueous solution is about 38%. Water is the only practical solvent because ammonium sulfate is practically insoluble in all other common solvents. Thus, while aqueous solutions are not satisfactory, there remains a need for a liquid ammonium sulfate product.
Another approach to preparing a liquid product is to make a suspension. However, in aqueous suspensions of ammonium sulfate, crystal dissolution and recrystallization occurs continually. This results in a progressive increase of the size of the particles and eventual settling.
U.S. Pat. No. 5,135,561 describes aqueous suspensions produced by mixing ammonium sulfate with ammonia and clay. U.S. Pat. No. 6,030,923 describes aqueous agricultural compositions optionally containing ammonium sulfate at concentrations up to 40 wt. %. U.S. Pat. No. 6,165,939 describes xe2x80x9csuspensoemulsionsxe2x80x9d optionally containing ammonium sulfate dissolved in the aqueous phase. U.S. Pat. No. 5,658,855 discloses aqueous herbicidal adjuvants optionally containing ammonium sulfate at concentrations up to 50 wt. %. U.S. Pat. No. 5,707,551 describes suspensions of water-soluble solids in water miscible (polar) liquids.
There appears to be no previous report of ammonium sulfate suspensions in hydrocarbons or non-polar oils. The literature on suspensions in hydrocarbon or other non-polar liquids is sparse. U.S. Pat. No. 3,793,015 and British patent GB 1151141 reported stable suspensions of particles such as carbon black in aliphatic hydrocarbons using metal salts of pyrophosphates and similar agents as dispersing agents. U.S. Pat. No. 3,317,635 described dispersions of polymer particles in organic liquids. U.S. Pat. No. 4,393,151 described suspensions of water-soluble polymers in a liquid hydrocarbon medium including a thickening agent.
There is little understanding of the fundamentals of suspensions. For instance, Yan et. al. state that, xe2x80x9cthe effect of particle size on the rheology of suspensions is a controversial subjectxe2x80x9d (Y. Yan, et. al., Chem, Eng. Sci., 46(4), 985-994, (1991)). Other authors have claimed that the shape and ionic character of the particles can be important factors. For instance, R. M. Turian, et. al. in a paper published in Powder Technology, 93, 219-223 (1997) suggests that the xe2x80x9cinterparticle interaction effects were quite strongxe2x80x9d for the suspensions he investigated. Therefore it is to be expected that different particles may present uniquely different properties.
Surfactants and soluble polymers are often used to stabilize suspensions of particles. These may function by adsorption on the particle surface and may provide steric interference which inhibits settling. However, the interaction between a particular liquid, particle, and surfactant is impossible to predict.
The liquid in an ammonium sulfate suspension intended for agricultural purposes must comply with government regulations, and should be qualified for use with pesticides under the Code of Federal Regulations (CFR). Mineral oils and a few other oils such as soybean oil are listed in 40 CFR 180.1001 paragraph c and have been used as adjuvants themselves. Petroleum distillates are also approved under this section of the CFR provided they conform to the conditions of 21 CFR 172.882 or 21 CFR 172.884.
Once a stable concentrated ammonium sulfate suspension is achieved, it can be useful for agricultural use only if it dissolves in water fairly quickly. It is known in the surfactant art that a hydrophilic surfactant is needed to break up and disperse oil in water but there are hundreds of different types. The hydrophilic character of a surfactant is measured by a hydrophile-lipophile balance (HLB) scale (See for example: Kirk-Othmer Encyclopedia of Chemical Technology, Second Edition, 8, 128-137, (1965)). Surfactants with a high HLB rating are hydrophilic or xe2x80x9cwater-lovingxe2x80x9d. Lower HLB surfactants are hydrophobic or oleophilic.
Very small particles of colloidal dimensions form stable suspensions even in dilute concentrations where hindered settling is not a factor. Colloidal particles are usually considered to be 0.001 mm (1 x micron) or less in diameter and form stable suspensions because of Brownian motion. However, the energy required to break down ammonium sulfate and most other materials to colloidal dimensions is extremely high and costly.
In the case of ammonium sulfate, there is a long-standing need to provide a low cost system that can form stable concentrated suspensions that are readily dispersible in water for use in agriculture and for other purposes.
The invention provides stable concentrated suspensions comprising ammonium sulfate, a surfactant, and an oil. The ammonium sulfate particles are at least about 99 wt. % passable through a Tyler #48 sieve. The surfactant is a non-ionic surfactant with an HLB rating from about 10 to about 15. The oil is a hydrocarbon or other non-polar oil having a viscosity of at least about 5 centipoises (cp) at 40xc2x0 C. The suspensions of the invention exhibit physical stability during normal storage conditions, and are readily dispersed in water.
In another embodiment, the ammonium sulfate suspensions of the invention additionally contain methylthio-xcex1-hyroxybutyric acid. It is surprisingly found that methylthio-xcex1-hyroxybutyric acid enhances the stability and reduces the viscosity of the ammonium sulfate suspensions of the invention.
In yet another embodiment, the ammonium sulfate suspensions of the invention additionally contain a solid herbicide.
Preferably, the suspensions of the invention, upon dilution in a suitable volume of water, are suitable for application to plants as herbicidal compositions, adjuvants in herbicidal compositions, or fertilizers, or may be used for other purposes. Weed-kill tests show that suspensions of the invention containing ammonium sulfate, mineral oil, and surfactant, diluted in water and in combination with an herbicide, exhibit synergistic effects in killing difficult weeds. Herbicide manufacturers usually recommend applying double the dose of herbicide when difficult weeds are present. However, from an environmental point of view it is more desirable to use less herbicide and an adjuvant to obtain the same effect. The suspensions of the invention meet that need.
Also and surprisingly, it has been found that the ammonium sulfate suspensions of the invention are compatible with water-soluble packaging whereas ammonium sulfate solids and aqueous solutions are not. This provides a distinct advantage in ease of use as the customer can drop a bag of pre-weighed chemicals into water without handling or measuring.